PURPOSE: To improve the quality of a seamless steel pipe by setting small the inclination angle of cross helical rolls in the stage of rolling at the prescribed time at the top and bottom of a material to be rolled thereby improving rolling efficiency and suppressing the generation of inside surface flaws.

CONSTITUTION: The cross helical rolls 1l, 1r in cross helical rolling of the seamless pipe are changed in the inclination angle β thereof by an automatic positioning device 8. An arithmetic control unit 6 drives the device 8 to increase the inclination angle of the rolls 1l, 1r up to β1 during the time since the material to be rolled is engaged with the rolls 1l, 1r until the material is rolled from the top to the length l1. The inclination angle is set at β2 larger than β1 up to the length l2. The inclination angle is set at the larger β3 in the stage of rolling the length l3 in the central part. The device 8 changes the inclination angle of the rolls 1l, 1r to β4 slightly smaller than the inclination angle β1 in the stage of rolling the top when a material position detector 9 detects the bottom. The stable piercing is made possible by the above-mentioned method.